ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2016) 45 OC3.2 | DOI: 10.1530/endoabs.45.OC3.2

A rare cause of rickets

Suma Uday & Nick Shaw

Department of Paediatric Endocrinology and Diabetes, Birmingham Children’s Hospital, Birmingham, UK.

Introduction: Nutritional rickets due to vitamin D and dietary calcium deficiency is common in the UK. However, nutritional rickets secondary to hypophosphataemia is rare. We present a rare case of hypophosphataemic rickets secondary to use of hydrolysed infant formula.

Case description: A 4 month old infant presented to ED with breathing difficulty. He was diagnosed to have bronchiolitis and admitted for further management.

He was born at 31 weeks by spontaneous vaginal delivery and required brief ventilatory support for the first 48 hours and was discharged home at 6 weeks. He had required repeated change in formula feeds due to constipation and recurrent vomiting. He was commenced on the hydrolysed formula Neocate for presumed cow’s milk protein allergy at the age of 3 months.

Investigations and management: A chest radiograph performed to assess for lower respiratory tract infection suggested rickets and was confirmed on a knee radiograph. There was no family history of rickets. There were no clinical features of rickets except for mild physiological bowing of legs. Investigations revealed a normal plasma calcium, raised alkaline phosphatase (1000 iu/l) and normal parathyroid hormone (24 ng/l) with reduced plasma phosphate (1.23 mmol/l). Vitamin D deficiency was excluded due to sufficient serum 25(OH) levels (60 nmol/l). Hypophosphataemic rickets was suspected. Tubular reabsorption of phosphate of 99.5% excluded renal tubular losses.

Outcome: In the absence of other causes of rickets, nutritional hypophosphataemic rickets secondary to poor absorption of phosphate on a hydrolysed formula was suspected. He was commenced on phosphate supplements and one alpha calcidol which was subsequently stopped as he had a raised 1,25 dihydroxyvitamin D(>250 pmol/l). The occurrence of hypophosphataemic rickets in the setting of the hydrolysed formula Neocate was confirmed following discussion with a colleague in the United States (case series awaiting publication).

Conclusion: Clinicians should exercise caution in the use of hydrolysed formula especially in the absence of objective evidence of cow’s milk protein allergy. Specialised formula feeds should be initiated following thorough investigations. Infants on hydrolysed formula should have close monitoring of growth and nutritional status.

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